There are abrasive tools and wear resistant parts that utilize diamond for its characteristic excellent hardness, heat conductivity, friction coefficient, etc. and that contribute to the improvement of productivity in many sectors of industry. Diamond in itself, with a high hardness that makes mechanical work very difficult, is favorably applied as a thin coating just to the work surface, where such properties are needed, of a ready base body with the shape finished.
High quality diamond film is prepared by plasma CVD. With hetero-epitaxial growth processes silicon has been mainly used as a substrate material, and molybdenum and platinum have also been used in a minor part. With such substrate materials, homo-epitaxial processes are also conducted for producing, by increasing the nucleation density, a dense and smooth deposit on diamond particles that are distributed in advance on the substrate as growth origins, instead of just relying upon the spontaneous nucleation.
With tungsten carbide alloys and some alloy steels that are favored materials for abrasive tools, on the other hand, it is considered to be impossible to deposit diamond layer directly on the surface thereof: carbon has a high diffusion tendency into cobalt and other iron group metals, which are contained in the material, and further carbon takes a graphite structure to become stabilized when present in contact with an iron group metal at high temperatures at atmospheric pressure, so no diamond particles can subsist in a CVD process if provided as growth origins in advance.
Thus conventional techniques require cobalt removal in advance from the surface of tungsten carbide alloy substrate, so as to prevent contact of diamond to be deposited with the iron group metal and thereby minimizing conversion to graphite during the process at a high temperature. Such step however inevitably decreases the substrate strength resulting from loss in cobalt bond material, failing to achieve the designed performance of the substrate.